Gases detected in super-Earth atmosphere

A video showing an artist's impression of the super-Earth orbiting its host star

Credit: ESA/Hubble, M. Kornmesser

Gases have been detected in the atmosphere of a super-Earth planet for the first time.

Astronomers analysed exoplanet 55 Cancri e using data gathered with the Hubble Space Telescope and found it has a dry atmosphere without any signs of water vapour, and that the atmosphere consists mainly of hydrogen and helium. 55 Cancri 3 is located about 40 lightyears from Earth.

Super-Earths are so-called because they have a greater mass than our own planet, but are still smaller than the gas giants in our Solar System. They are thought to be the most common type of planet in the Milky Way.

"This is a very exciting result because it’s the first time that we have been able to find the spectral fingerprints that show the gases present in the atmosphere of a super-Earth,” says Angelos Tsiaras, a PhD student at UCL. “The observations of 55 Cancri e’s atmosphere suggest that the planet has managed to cling on to a significant amount of hydrogen and helium from the nebula from which it originally formed.”

55 Cancri e orbits close to its parent star, which is uncommon for the super-Earths that we know about. Its year lasts just 18 hours and temperatures on the surface are thought to reach about 2000°C. This proximity to the host star enabled the team at UCL to use a new method of analysis during its transits.

Using the Wide Field Camera 3, the astronomers scanned across the star to create a number of spectra, and thus retrieved the spectrum of the super-Earth from the light of its star.

The data showed small traces of hydrogen cyanide, which could indicate a carbon-rich atmosphere.

“If the presence of hydrogen cyanide and other molecules is confirmed in a few years time by the next generation of infrared telescopes, it would support the theory that this planet is indeed carbon rich and a very exotic place,” says Jonathan Tennyson, UCL. “Although hydrogen cyanide, or prussic acid, is highly poisonous, so it is perhaps not a planet I would like to live on!”

Read more about the atmospheres of exoplanets in the March issue of BBC Sky at Night Magazine, out 18 February.

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